Domestic cats are furry murderers, argues a New Zealand businessman who is spearheading a campaign to get his fellow Kiwis to give them up.

'Save a Kaka, kill your cat' is the message of New Zealand businessman Gareth Morgan, who has started a campaign to rid the ecologically isolated islands of murderous felines in attempt to stem the dwindling numbers of native birds.

For 80 million years, the archipelago has been separated by ocean from any other land. Apart from one mouse-sized animal which went extinct around 16 million years ago, there have never been any land mammals on the islands (although there remain two species of native bat, and plenty of whales, dolphins and seals). That left an ecological niche which was largely filled by birds, being some of the few animals which could reach the islands after the seas split them from the rest of Gondwanaland.

New Zealand has some of the most unique, and clueless, birds in the world. The Kakapo is a giant green parrot which eats grass and has sex with Stephen Fry's head. The Kiwi is the size of a chicken, and lays an egg so big that the female, for the last couple of days of her incubation, has no room for any food in her stomach and must fast. The Kokako is a semi-flightless bird which sings duets in breeding pairs for hours on end and occupies the same niche as a flying squirrel.

None of them were ever exposed to predatory land mammals until the Maori arrived in the 14th century, and so they have very few natural defences against them. The introduction of mice and rats was bad enough, but once cats appeared, it was nearly over. The Kakapo and Kiwi are now critically endangered species, each limited to a few islands which have been cleared of introduced predators — but there's hope for the Kokako, as well as the Kaka and Weka which are also under threat. And one thing which would help is New Zealanders giving up their cats.

Gareth Morgan has started a campaign, Cats to Go, which is pushing for that aim. He writes:

New Zealand is the last refuge of a huge range of bird species, we’re famous for our claim to be clean and green, and some of us have recognised the huge economic benefit, let alone the ecological dividend, from achieving a Predator Free New Zealand.

But the vision is flawed. Almost half of Kiwi households have a cat (or two) making New Zealanders the world’s biggest cat owners. Cats are incredibly effective hunters and are wiping out our native birds.

… Like the parent of a bully saying that their little Johnny would not behave like that, if you’re a cat owner reading this, you are probably thinking that the above statistics don’t apply to your cat. The fact is that your furry friend is actually a friendly neighbourhood serial killer.

He doesn't actually want people to kill their cats directly — though he emphasises that "that is an option" — instead proposing that people put bells on their cats to warn birds, keep them inside, get them neutered, and, above all, not replace them when they die.

Even if it works, there is a long way to go to make New Zealand safe for its native birds. Rats, mice and possums are all widespread and causing damage of their own. But a cat-free New Zealand might still be worth fighting for.